IEC 62765-2:2019

Nuclear power plants - Instrumentation and control important to safety - Management of ageing of sensors and transmitters - Part 2: Temperature sensors

IEC 62765-2:2019 identifies minimum requirements and applicable practices for correcting and preventing any potential impacts on nuclear power plant (NPP) safety due to the ageing of temperature sensors, such as NPP resistance temperature detectors (RTDs) and thermocouples (TCs).
This document provides strategies, technical requirements, and recommended practices for the management of the ageing of temperature sensors important to safety in nuclear power plants (NPPs) to ensure that ageing can be identified and that suitable remedial actions are undertaken as necessary to demonstrate that the safety of the plant will not be impaired. This document is aligned with IEC 62342, which provides guidance on ageing management for instrumentation and control (I&C) systems important to safety in NPPs

Centrales nucléaires de puissance - Instrumentation et contrôle-commande importants pour la sûreté - Gestion du vieillissement des capteurs et des transmetteurs - Partie 2: Capteurs de température

l'IEC 62765-2:2019 identifie les exigences minimales et les pratiques applicables pour la correction et la prévention des effets possibles sur la sûreté des centrales nucléaires de puissance (CNP) dus au vieillissement des capteurs de température, tels que les sondes à résistance (SR) et les couples thermoélectriques (TC) de ces centrales.
Le présent document fournit les stratégies, les exigences techniques et les pratiques recommandées pour la gestion du vieillissement des capteurs de température importants pour la sûreté dans les centrales nucléaires de puissance pour s'assurer que le vieillissement peut être identifié et que les actions pour y remédier sont mises en œuvre lorsque cela est nécessaire pour démontrer que la sûreté de l'installation ne sera pas dégradée. Le présent document est aligné avec l'IEC 62342 qui fournit des recommandations sur la gestion du vieillissement des systèmes d'instrumentation et de contrôle-commande (I&C) importants pour la sûreté dans les centrales nucléaires de puissance.

General Information

• Status: Published
• Publication Date: 28-Jan-2019
• ICS: 27.120.20 - Nuclear power plants. Safety
• Technical Committee: SC 45A - Instrumentation, control and electrical power systems of nuclear facilities
• Drafting Committee: WG 10 - TC 45/SC 45A/WG 10
• Current Stage: PPUB - Publication issued
• Start Date: 29-Jan-2019
• Completion Date: 19-Oct-2018

Overview

IEC 62765-2:2019 is an international standard focusing on the management of ageing of temperature sensors that are critical for the safety instrumentation and control systems in nuclear power plants (NPPs). This standard outlines the minimum requirements and best practices essential for identifying, correcting, and preventing safety impacts that might arise from the ageing of temperature sensors such as Resistance Temperature Detectors (RTDs) and thermocouples (TCs).

The document is a part of the broader IEC 62765 series that addresses ageing management of sensors and transmitters important to safety in nuclear power plants. It aligns closely with IEC 62342, which provides overarching guidance on ageing management for instrumentation and control (I&C) systems within these plants.

Key Topics

• Ageing Effects on Temperature Sensors
  Detailed insight into how environmental stressors and operational conditions contribute to the degradation of temperature sensors in NPPs.

• Types of Temperature Sensors Covered

  • Resistance Temperature Detectors (RTDs)
  • Thermocouples (TCs)
    Including their characteristics as defined in IEC standards.

• Ageing Management Methodology
  Strategies and processes to monitor, detect, evaluate, and mitigate sensor ageing. This includes:

  • Performance verification tests
  • Inspection and calibration intervals
  • Validation of test methods
  • Replacement and corrective action guidelines

• Technical Requirements
  Specifications for interfaces such as thermowells, cables, and connectors that impact sensor reliability and ageing.

• Performance Verification and Calibration
  Procedures for onsite calibration and testing to ensure sustained sensor accuracy and safety system integrity.

• Documentation and Traceability
  Importance of systematic documentation of calibration, testing, and maintenance activities to support safety analyses and regulatory compliance.

Applications

IEC 62765-2:2019 applies primarily to the nuclear power generation sector, where temperature sensors play a vital role in safety instrumentation and control. Its practical applications include:

• Safety System Reliability
  Ensures that ageing temperature sensors continue to perform within specified safety tolerances, maintaining the integrity of reactor cooling systems and other critical processes.

• Ageing Management Programs (AMPs)
  Provides nuclear facility operators with a framework for establishing and updating ageing management programs targeting temperature sensors to achieve sustained plant safety.

• Regulatory Compliance
  Assists plants in meeting national and international regulatory requirements related to instrumentation ageing and safety critical component management.

• Predictive Maintenance
  Enables proactive identification of sensor degradation trends facilitating timely maintenance or replacement, reducing unexpected downtime and enhancing plant availability.

Related Standards

• IEC 62342 – Instrumentation and control systems ageing management guidelines, providing the overall framework for I&C ageing management in nuclear facilities.

• IEC 62651 Series – Standards concerning thermocouples, including design and testing requirements.

• IAEA Safety Standards – Including ageing management guidelines related to instrumentation important to safety in nuclear power plants.

• IEC 60751 – International standard on industrial platinum resistance temperature detectors (RTDs), relevant for sensor specification.

Summary

IEC 62765-2:2019 offers a comprehensive approach to controlling and managing the ageing of temperature sensors important to nuclear power plant safety. Following this standard enables plant operators to effectively detect performance degradation, implement appropriate maintenance actions, and maintain compliance with safety regulations. Integrating IEC 62765-2:2019 into ageing management programs promotes reactor safety, reliability, and long-term operational performance, ensuring that critical temperature sensors continue to operate accurately throughout their service life.

Standards Content (Sample)

IEC 62765-2 ®
Edition 1.0 2019-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Nuclear powers plants – Instrumentation and control important to safety –
Management of ageing of sensors and transmitters –
Part 2: Temperature sensors
Centrales nucléaires de puissance – Instrumentation et contrôle-commande
importants pour la sûreté – Gestion du vieillissement des capteurs et des
transmetteurs –
Partie 2: Capteurs de température

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de l'IEC ou du Comité national de l'IEC du pays du demandeur. Si vous avez des
questions sur le copyright de l'IEC ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez
les coordonnées ci-après ou contactez le Comité national de l'IEC de votre pays de résidence.

IEC Central Office Tel.: [phone]
3, rue de Varembé [e-mail]
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.

IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing 21 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 16 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.

IEC publications search - webstore.iec.ch/advsearchform IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a 67 000 electrotechnical terminology entries in English and
variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and

CISPR.
IEC Just Published - webstore.iec.ch/justpublished

Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: [e-mail].
A propos de l'IEC
La Commission Electrotechnique Internationale (IEC) est la première organisation mondiale qui élabore et publie des
Normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications IEC
Le contenu technique des publications IEC est constamment revu. Veuillez vous assurer que vous possédez l’édition la
plus récente, un corrigendum ou amendement peut avoir été publié.

Catalogue IEC - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
Application autonome pour consulter tous les renseignements
Le premier dictionnaire en ligne de termes électroniques et
bibliographiques sur les Normes internationales,
électriques. Il contient 21 000 termes et définitions en anglais
Spécifications techniques, Rapports techniques et autres
et en français, ainsi que les termes équivalents dans 16
documents de l'IEC. Disponible pour PC, Mac OS, tablettes
langues additionnelles. Egalement appelé Vocabulaire
Android et iPad.
Electrotechnique International (IEV) en ligne.

Recherche de publications IEC -
Glossaire IEC - std.iec.ch/glossary
webstore.iec.ch/advsearchform
67 000 entrées terminologiques électrotechniques, en anglais
La recherche avancée permet de trouver des publications IEC et en français, extraites des articles Termes et Définitions des
en utilisant différents critères (numéro de référence, texte, publications IEC parues depuis 2002. Plus certaines entrées
comité d’études,…). Elle donne aussi des informations sur les antérieures extraites des publications des CE 37, 77, 86 et
projets et les publications remplacées ou retirées. CISPR de l'IEC.

IEC Just Published - webstore.iec.ch/justpublished Service Clients - webstore.iec.ch/csc
Restez informé sur les nouvelles publications IEC. Just Si vous désirez nous donner des commentaires sur cette
Published détaille les nouvelles publications parues. publication ou si vous avez des questions contactez-nous:
Disponible en ligne et aussi une fois par mois par email. [e-mail].

IEC 62765-2 ®
Edition 1.0 2019-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Nuclear powers plants – Instrumentation and control important to safety –

Management of ageing of sensors and transmitters –

Part 2: Temperature sensors
Centrales nucléaires de puissance – Instrumentation et contrôle-commande

importants pour la sûreté – Gestion du vieillissement des capteurs et des

transmetteurs –
Partie 2: Capteurs de température

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.120.20 ISBN 978-2-8322-6171-2

– 2 – IEC 62765-2:2019 © IEC 2019
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 Abbreviated terms . 13
5 Technical background . 13
5.1 General . 13
5.2 Type of the sensors in IEC standards . 14
5.2.1 General . 14
5.2.2 RTDs in IEC standards . 14
5.2.3 Thermocouples in IEC standards . 14
5.3 Interface between the sensors and process in IEC standards . 15
5.3.1 Thermowell . 15
5.3.2 Cable connectors for temperature sensors . 15
5.3.3 Cables of temperature sensors . 15
5.3.4 Sheath for temperature sensor cable . 15
5.4 Ageing effects of temperature sensors . 16
5.5 Environmental stressors . 16
5.6 Techniques for detecting temperature sensor ageing . 17
6 Ageing management of temperature sensors . 17
6.1 General . 17
6.2 Methodology of ageing management . 18
6.3 Ageing management program for temperature sensors . 18
6.4 Identification and assessment of ageing by performance verification tests . 19
6.5 Test and inspection interval . 19
6.6 Test location . 19
6.7 Calibration of measurement and test equipment (M&TE) . 19
6.8 Test and inspection results . 20
6.9 Validation of test methods . 20
6.10 Classification of condition monitoring system and its software . 20
6.11 Replacement of sensor or its parts . 20
7 Acceptable means for sensor testing . 20
8 Relationship between initial qualification and sensor ageing management . 21
Annex A (informative) Performance verification of temperature sensors . 22
A.1 Tests – Verification of performance . 22
A.2 Calibration test of temperature sensors . 23
A.2.1 General . 23
A.2.2 Comparison of traditional calibration and online calibration method . 23
A.3 Response time testing . 24
A.4 Uncertainty of elements for the sensors . 24
A.5 Corrective actions for inoperable sensors . 25
A.6 Alternative method with online testing . 26
A.7 Documentation of calibration . 26
Annex B (informative) IAEA and IEC standards related to ageing management of the
sensors . 27

Annex C (informative) Tolerances of temperature sensors in international standards . 28
C.1 General . 28
C.2 ITS-90. 28
C.3 Tolerance classes of temperature sensors . 28
C.4 Calibration tolerance . 29
Annex D (informative) Development of a plant ageing management program of
temperature sensors . 30
D.1 General . 30
D.2 Key steps for AMP of temperature sensors . 30
D.3 Ageing management program . 31
Bibliography . 33

Figure 1 – Schematic diagram of a TC (sourced from IEC 62651) . 14
Figure 2 – Conceptual methodology of ageing management processes . 18

Table 1 – Examples of ageing effects and their potential causes . 16
Table 2 – Examples of environmental stressors with potential consequence . 17
Table A.1 – Consideration for verification of performance test . 22
Table A.2 – Type test, routine test, and additional test for RTD . 23
Table A.3 – Comparison of concerns of calibration methods . 24
Table A.4 – Examples of uncertainty issues for RTDs . 25
Table A.5 – Required example actions followed by acceptance criteria . 25
Table B.1 – IAEA standards related to ageing management . 27
Table B.2 – Ageing management standards for the sensors in IEC standards . 27
Table C.1 – Tolerance classes of typical temperature sensors . 29
Table D.1 – Key steps for the ageing management program of temperature sensors . 31
Table D.2 – An example of AMP guidance sheet for the sensors . 32

– 4 – IEC 62765-2:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWERS PLANTS –
INSTRUMENTATION AND CONTROL IMPORTANT TO SAFETY –
MANAGEMENT OF AGEING OF SENSORS AND TRANSMITTERS –

Part 2: Temperature sensors
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62765-2 has been prepared by subcommittee 45A:
Instrumentation, control and electrical power systems of nuclear facilities, of IEC technical
committee 45: Nuclear instrumentation.
The text of this International Standard is based on the following documents:
FDIS Report on voting
45A/1218/FDIS 45A/1227/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts in the IEC 62765 series, published under the general title Nuclear power
plants – Instrumentation and control important to safety – Management of ageing of sensors
and transmitters, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC 62765-2:2019 © IEC 2019
INTRODUCTION
a) Technical background, main issues, and organisation of the standard
With the majority of NPPs over 30 years old, the management of ageing of temperature
sensors is currently a relevant topic, especially for those plants that have extended their
operating licenses or are considering this option. This standard is intended to be used by
operators of NPPs (utilities), systems evaluators, vendors, and by licensors. In the
international temperature measurement, the scale of temperature has been updated with ITS-
90 since it was published in 1990, so it is necessary that ITS-90 should be addressed in the
standard to cover the calibration of measuring and test equipment for temperature sensors.
b) Situation of the current standard in the structure of the IEC SC 45A standard series
IEC 62765 is the third level IEC SC 45A document comprised of several parts to tackle the
specific issue of management of ageing of sensors and transmitters in nuclear power plants
(NPPs) for I&C systems important to safety. Part 2 of IEC 62675 is dedicated to temperature
sensors.
IEC 62342 is the second level standard of SC 45A covering the domain of the management of
ageing of nuclear instrumentation systems used in NPPs to perform functions important to
safety. IEC 62342 is the introduction to a series of standards to be developed by IEC SC 45A
covering the management of the ageing of specific I&C systems or components such as
electrical cabling systems (IEC 62465), and sensors and transmitters (IEC 62765).
IEC 62765-2 is to be read in association with IEC 62342 and IEC TR 62096, which is the
appropriate IEC SC 45A Technical Report that provides guidance on the decision for
modernisation when the management of ageing techniques is no longer successful. For more
details on the structure of the IEC SC 45A standard series, see item d) of this introduction.
c) Recommendations and limitations regarding the application of this standard
It is important to note that this standard establishes no additional functional requirements for
safety systems. Ageing mechanisms have to be prevented and thus identified by performance
measurements in order to minimize their impact on sensor reliability. Aspects for which
special recommendations and limitations have been provided in this standard are:
• criteria for the evaluation of ageing of temperature sensors in NPPs;
• steps to be followed to establish the temperature sensor testing requirements for an
ageing management program for NPP instrumentation systems; and
• relationships between on-going qualification analysis and ageing management program
with regard to temperature sensors.
It is recognised that testing and monitoring techniques used to evaluate the ageing condition
of NPPs’ sensors and transmitters are continuing to develop at a rapid pace and that it is not
possible for a standard such as this to include references to all modern technologies and
techniques.
This standard identifies minimum requirements aimed at ensuring that any potential impacts
on NPP safety due to the ageing of temperature sensors of NPPs can be identified and that
suitable actions are undertaken to demonstrate that the safety of the plant will not be
impaired. To ensure that this standard will continue to be relevant in future years, the
emphasis has been placed on issues of principle, rather than specific technologies.
d) Description of the structure of the IEC SC 45A standard series and relationships
with other IEC documents and other bodies documents (IAEA, ISO)
The top-level documents of the IEC SC 45A standard series are IEC 61513 and IEC 63046.
IEC 61513 provides general requirements for I&C systems and equipment that are used to
perform functions important to safety in NPPs. IEC 63046 provides general requirements for
electrical power systems of NPPs; it covers power supply systems including the supply

systems of the I&C systems. IEC 61513 and IEC 63046 are to be considered in conjunction
and at the same level. IEC 61513 and IEC 63046 structure the IEC SC 45A standard series
and shape a complete framework establishing general requirements for instrumentation,
control and electrical systems for nuclear power plants.
IEC 61513 and IEC 63046 refer directly to other IEC SC 45A standards for general topics
related to categorization of functions and classification of systems, qualification, separation,
defence against common cause failure, control room design, electromagnetic compatibility,
cybersecurity, software and hardware aspects for programmable digital systems, coordination
of safety and security requirements and management of ageing. The standards referenced
directly at this second level should be considered together with IEC 61513 and IEC 63046 as
a consistent document set.
At a third level, IEC SC 45A standards not directly referenced by IEC 61513 or by IEC 63046
are standards related to specific equipment, technical methods, or specific activities. Usually
these documents, which make reference to second-level documents for general topics, can be
used on their own.
A fourth level extending the IEC SC 45A standard series, corresponds to the Technical
Reports which are not normative.
The IEC SC 45A standards series consistently implement and detail the safety and security
principles and basic aspects provided in the relevant IAEA safety standards and in the
relevant documents of the IAEA nuclear security series (NSS). In particular this includes the
IAEA requirements SSR-2/1, establishing safety requirements related to the design of nuclear
power plants (NPPs), the IAEA safety guide SSG-30 dealing with the safety classification of
structures, systems and components in NPPs, the IAEA safety guide SSG-39 dealing with the
design of instrumentation and control systems for NPPs, the IAEA safety guide SSG-34
dealing with the design of electrical power systems for NPPs and the implementing guide
NSS17 for computer security at nuclear facilities. The safety and security terminology and
definitions used by SC 45A standards are consistent with those used by the IAEA.
IEC 61513 and IEC 63046 have adopted a presentation format similar to the basic safety
publication IEC 61508 with an overall life-cycle framework and a system life-cycle framework.
Regarding nuclear safety, IEC 61513 and IEC 63046 provide the interpretation of the general
requirements of IEC 61508-1, IEC 61508-2 and IEC 61508-4, for the nuclear application
sector. In this framework IEC 60880, IEC 62138 and IEC 62566 correspond to IEC 61508-3
for the nuclear application sector. IEC 61513 and IEC 63046 refer to ISO as well as to IAEA
GS-R part 2 and IAEA GS-G-3.1 and IAEA GS-G-3.5 for topics related to quality assurance
(QA). At level 2, regarding nuclear security, IEC 62645 is the entry document for the
IEC SC 45A security standards. It builds upon the valid high level principles and main
concepts of the generic security standards, in particular ISO/IEC 27001 and ISO/IEC 27002; it
adapts them and completes them to fit the nuclear context and coordinates with the
IEC 62443 series. At level 2, IEC 60964 is the entry document for the IEC/SC 45A control
rooms standards and IEC 62342 is the entry document for the ageing management standards.
NOTE 1 It is assumed that for the design of I&C systems in NPPs that implement conventional safety functions
(e.g. to address worker safety, asset protection, chemical hazards, process energy hazards) international or
national standards would be applied.
NOTE 2 IEC SC 45A domain was extended in 2013 to cover electrical systems. In 2014 and 2015 discussions
were held in IEC SC 45A to decide how and where general requirements for the design of electrical systems were
to be considered. IEC SC 45A experts recommended that an independent standard be developed at the same level
as IEC 61513 to establish general requirements for electrical systems. Project IEC 63046 is now launched to cover
this objective. When IEC 63046 is published this NOTE 2 of the introduction of IEC SC 45A standards will be
suppressed.
– 8 – IEC 62765-2:2019 © IEC 2019
NUCLEAR POWERS PLANTS –
INSTRUMENTATION AND CONTROL IMPORTANT TO SAFETY –
MANAGEMENT OF AGEING OF SENSORS AND TRANSMITTERS –

Part 2: Temperature sensors
1 Scope
This part of IEC 62765 identifies minimum requirements and applicable practices for
correcting and preventing any potential impacts on nuclear power plant (NPP) safety due to
the ageing of temperature sensors, such as NPP resistance temperature detectors (RTDs)
and thermocouples (TCs).
This document provides strategies, technical requirements, and recommended practices for
the management of the ageing of temperature sensors important to safety in nuclear power
plants (NPPs) to ensure that ageing can be identified and that suitable remedial actions are
undertaken as necessary to demonstrate that the safety of the plant will not be impaired. This
document is aligned with IEC 62342, which provides guidance on ageing management for
instrumentation and control (I&C) systems important to safety in NPPs.
IEC 62765 standard series covers pressure transmitters (Part 1) and temperature sensors
(Part 2). Part 1 covers pressure transmitter (PT), level transmitter (LT) and flow transmitter
(FT). Part 2 consists of resistance temperature detector (RTD) and thermocouple (TC) with
respect to instrumentation and control (I&C) important to safety. Detector of neutron power
(Part 3) will be covered in a separate standard.
Interfaces of temperature sensors with processes such as thermowells, seals, sheathes,
extension/compensating cables, and connectors are within the scope of this document.
Ageing management of temperature sensors used as M&TEs are beyond the scope of this
document.
Temperature units of this document are in terms of International Temperature Scale-1990
(ITS- 90), because of consistency with normative references.
IAEA SSR-2/1 and SSR-2/2 address the requirements of ageing management in the design,
as well as in the operation of the lifetime of the plant.SSG-39 recommends design
consideration for ageing management specific to I&C system.
The requirements of temperature sensors for industrial and nuclear application in the
normative references are indispensable to this document whereas this document focuses on
the ageing management of temperature sensors to meet the requirements.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 60584-1:2013, Thermocouples – Part 1: EMF specifications and tolerances
IEC 60584-3:2007, Thermocouples – Part 3: Extension and compensating cables –
Tolerances and identification system

IEC 60671:2007, Nuclear power plants – Instrumentation and control systems important to
safety – Surveillance testing
IEC 60737:2010, Nuclear power plants – Instrumentation important to safety – Temperature
sensors (in-core and primary coolant circuit) – Characteristics and test methods
IEC 60751:2008, Industrial platinum resistance thermometers and platinum temperature
sensors
IEC/IEEE 60780-323:2016, Nuclear facilities – Electrical equipment important to safety –
Qualification
IEC 61226:2009, Nuclear power plants – Instrumentation and control important to safety –
Classification of instrumentation and control functions
IEC 61515:2016, Mineral insulated metal-sheathed thermocouple cables and thermocouples
IEC 62138:2004, Nuclear power plants – Instrumentation and control important to safety –
Software aspects for computer-based systems performing category B or C functions
IEC 62342:2007, Nuclear power plants – Instrumentation and control systems important to
safety – Management of ageing
IEC 62385:2007, Nuclear power plants – Instrumentation and control important to safety –
Methods for assessing the performance of safety system instrument channels
IEC 62397:2007, Nuclear power plants – Instrumentation and control important to safety –
Resistance temperature detectors
IEC 62465:2010, Nuclear power plants – Instrumentation and control important to safety –
Management of ageing of electrical cabling system
IEC/IEEE 62582-1:2011, Nuclear power plants – Instrumentation and control important to
safety – Electrical equipment condition monitoring methods – Part 1: General
IEC 62651:2013, Nuclear power plants – Instrumentation important to safety –
Thermocouples: Characteristics and test methods
IAEA Safety Standard Series No. SSR-2/1:2016, Safety of Nuclear Power Plant: Design,
specific safety requirements
IAEA Safety Standard Series No. SSR-2/2:2016, Safety of Nuclear Power Plant:
Commissioning and Operation, specific safety requirements
IAEA Safety Standard Series No. NS-G-2.12:2009, Ageing management for nuclear power
plants: safety guide
IAEA Specific Safety Guide No. SSG-39:2016, Design of instrumentation and control systems
for nuclear power plants
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

– 10 – IEC 62765-2:2019 © IEC 2019
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
adjustment
set of operations carried out on a measuring instrument in order that it provides given
indications corresponding to given values of the measurand
Note 1 to entry: An adjustment can be carried out during cross-calibration of temperature sensors in the
temperature measurement channel.
[SOURCE: IEC 60050-311:2001, 311-03-16]
3.2
calibration
set of operations that establish, under specified conditions, the relationship between values of
quantities indicated by a measuring instrument or measuring system, or values represented
by a material measure or a reference material, and the corresponding values realized by
measurement standards
[SOURCE: IAEA Safety Glossary, edition 2016]
3.3
calibration diagram
portion of the co-ordinate plane, defined by the axis of indication and the axis of results of
measurement, which represents the response of the instrument to different values of the
measurand
[SOURCE: IEC 60050-311:2001, 311-01-10]
3.4
compensating cables
manufactured from conductors having a composition different from the corresponding
thermocouple. They are designated by the letter "C" following the designation of the
thermocouple, for example "KC". In some cases different tolerances apply for the same
thermocouple type over different temperature ranges. These are distinguished by additional
letters such as, for example, KCA and KCB
[SOURCE: IEC 60584-3:2007, 3.1.2]
3.5
cross-calibration
procedure of inter-comparing the indications of redundant instruments (e.g., temperature
sensors) to identify outlier sensors as a means of verifying calibration or identifying calibration
changes. A more appropriate term for this definition is "cross-validation," although cross-
calibration is more commonly used
Note 1 to entry: A calibration test of temperature sensors in some NPPs can be different from this definition
mainly because an adjustment of the temperature channel during cross-calibration may be allowed within a
predetermined allowable value.
[SOURCE: IEC 62385:2007, 3.6]
3.6
drift
change in the indication of a measuring instrument, generally slow, continuous, not
necessarily in the same direction and not related to a change in the measurand

Note 1 to entry: Stability and shift are sometimes used interchangeably with drift.
[SOURCE: IEC 60050-311:2001, 311-06-13]
3.7
electromagnetic interference
EMI
degradation of the performance of an equipment, transmission channel or system caused by
an electromagnetic disturbance
[SOURCE: IEC 60050-161:1990, 161-01-06]
3.8
extension and compensating cables
cables used for the electrical connection between the open ends of a thermocouple and the
reference junction in those installations where the conductors of the thermocouple are not
directly connected to the reference junction. The thermoelectric properties of extension and
compensating cables shall be close to the properties of the corresponding thermocouple
[SOURCE: IEC 60584-3:2007, 3.1]
3.9
extension cables
cables manufactured from conductors having the same nominal composition as those of the
corresponding thermocouple. They are designated by the letter "X" following the designation
of the thermocouple, for example "JX"
[SOURCE: IEC 60584-3:2007, 3.1.1]
3.10
measurand
particular quantity subject to measurement
[SOURCE: IEC 60050-311:2001, 311-01-03]
3.11
platinum resistance thermometer
PRT
temperature responsive device consisting of one or more sensing platinum resistors within a
protective sheath, internal connecting wires and external terminals to permit connection of
electrical measurement instruments. Mounting means and connection heads may be included.
Not included is any separable protection tube or thermowell
Note 1 to entry: The term PRT also refers to "resistance temperature detector (RTD)".
[SOURCE: IEC 60751:2008, 3.5]
3.12
resistance temperature detector
RTD
detector generally made up of a stainless steel cylindrical barrel protecting a platinum resistor
whose resistance varies with temperature. This detector is placed in the piping containing the
fluid whose temperature is measured in this way. It can be directly immersed in the fluid or
protected by an intermediate casing called the thermowell
[SOURCE: IEC 62397:2007, 3.5]
– 12 – IEC 62765-2:2019 © IEC 2019
3.13
response time
period of time necessary for a component to achieve a specified output state from the time
that it receives a signal requiring it to assume that output state
[SOURCE: IAEA Safety Glossary, 2016 edition]
3.14
self-heating error
rise in the indicated temperature due to the power dissipated in the sensor
[SOURCE: IEC 62397:2007, 3.7]
3.15
sensor
measuring element; part of a measuring instrument, or measuring chain, which is directly
affected by the measurand and which generates a signal related to the value of the
measurand
[SOURCE: IEC 60050-311:2001, 311-05-01]
3.16
thermocouple
TC
pair of conductors of dissimilar materials joined at one end and forming part of an
arrangement using the thermoelectric effect for temperature measurement
[SOURCE: IEC 60584-1:2013, 2.3]
3.17
thermoelectric effect
Seebeck effect
production of an electromotive force EMF due to the difference of temperature between two
junctions of different metals or alloys forming part of the same circuit
Note 1 to entry: The term Seebeck also refers to " thermoelectric effect".
[SOURCE: IEC 60584-1:2013, 2.1]
3.18
thermowell
protective jacket for temperature sensors (RTDs and TCs). The thermowell is also used to
facilitate replacement of temperature sensor
[SOURCE: IEC 62385:2007, 3.19]
3.19
tolerance of RTD
initial maximum allowable deviation expressed as temperature in ℃ from nominal
temperature/resistance relationship in RTD
3.20
tolerance of TC
initial maximum allowable deviation from the EMF specification of thermocouple
Note 1 to entry: The tolerance is expressed as the temperature equivalent, in °C.

4 Abbreviated terms
AFV As Found Value
AV Allowable Value
AMP Ageing Management Program
CT Calibration Tolerance
DBE Design Basis Event
EMF Electromotive Force
EMI Electromagnetic Interference
EQ Equipment Qualification
FSAR Final Safety Analysis Report
HELB High Energy (Steam) Line Break
IR Insulation Resistance
ITS-90 The International Temperature Scale of 1990
LCSR Loop Current Step Response
MIMS Mineral Insulated Metal Sheathed
M&TE Measurement and Test Equipment
NPP Nuclear Power Plant
PRT Platinum Resistance Thermometer
PT Pressure Transmitter
R&D Research and Development
RTD Resistance Temperature Detector
QA Quality Assurance
TC Thermocouple
V&V Verification and Validation
5 Technical background
5.1 General
IAEA SSR-2/1 describes the requirements of ageing management in the design for safe
operation over a lifetime. It is also necessary that a design margin be provided to take
account of the ageing mechanism, neutron embrittlement, and wear out, as well as the
potential for ageing degradation. SSR-2/2 also requires an effective ageing management
program over the operating lifetime of the plant. Subclauses 6.135 to 6.152 of SSG-39:2016
recommend design consideration for ageing management specific to I&C systems to meet the
requirements of SSR-2/1.
The baseline of requirements of ageing management is to understand and identify the ageing
phenomena, which cover the ageing mechanism, causes and potential effects of temperature
sensors. Annex A summarises various kinds of tests for performance verification in order to
identify a degradation in lifetime and to assess an ageing mechanism. IEC 62342 guides the
general aspect of ageing management of instruments including temperature sensors, whereas
IEC 60737 and others listed in Annex B cover characteristics and test methods of temperature
sensors. Existing IAEA and IEC standards for ageing management standards are summarised
in Annex B.
– 14 – IEC 62765-2:2019 © IEC 2019
Performance tests in Annex A are important because they can detect ageing effects.
Acceptance criteria for tests of temperature sensors are a critical element of an ageing
management program (AMP) and they should be understood to identify the ageing effects, to
evaluate the ageing problem, and to take a corrective action. The specified temperature
tolerances of temperature sensors used as a basis for acceptance criteria for calibration tests
are summarised in Annex C. Key steps and an example of AMP sheet are shown in Annex D.
5.2 Type of the sensors in IEC standards
5.2.1 General
TCs and RTDs are both used for the temperature measurement of fluid, steam, or gas in the
process of NPPs. The choice of TC versus RTD depends on the application and requirements
for accuracy, response time, repeatability, linearity, and other factors.
The difference of accuracy or tolerance between PTs and temperature sensors is as follows:
• Expression of accuracy of PTs: percentile of full span, the same within a full span.
• Expression of accuracy of temperature sensors: not the same within a full span, but
constant within a specific temperature range and linearly dependent on measuring
temperature beyond the range.
5.2.2 RTDs in IEC standards
An RTD consists of a wired coil or deposited film of pure metal, commonly platinum, whose
resistance changes with temperature. IEC 60737 describes the requirements of qualification
tests and other design type tests of the temperature sensors in NPPs. IEC 60751 specifies
temperature tolerances for each class of RTD, temperature/resistance relationship (i.e. a
reference calibration diagram), and acceptance criteria for type tests and routine tests.
IEC 60751 has been used widely as an industrial RTD standard. IEC 62397 specifies
environmental qualification and other requirements for RTDs in NPPs.
5.2.3 Thermocouples in IEC standards
Thermocouples are temperature-sensitive elements that convert thermal difference into
electric voltage. The principle is to measure an EMF voltage between two dissimilar
conductors. Metal A and Metal B in Figure 1 have a contact potential; i.e. EMF between them,
and the EMF changes as the tempe
...